Chemical milling is a stationary non-combustion source of nitrogen oxide gases that contaminate the atmosphere. Noxious nitrogen oxide fumes are generated in copious amounts when steel, stainless steel, nickel, titanium and other various alloys are dissolved in acid solutions. These acid solutions are generally aqua regia except in the case of titanium where hydrofluoric acid is used in lieu of hydrochloric acid. In either case, the principal effluent gases are nitrogen oxides. Substantial control of nitrogen oxide fumes from any such milling operation is possible by enclosing the area of vapor production over the acid solution in which workpieces are immersed. (Brevik U.S. Pat. No. 3,320,105). In prevalent commercial usage, the present state of the art utilizes open tank milling with any noxious fumes being pumped away to be treated.
This invention generally relates to a complete enclosure of the milling process, thus allowing complete control of noxious fumes and providing a safe environment for personnel associated with the process. This apparatus can be distinguished from that used in the Brevik apparatus by its complete physical, vapor-tight enclosure of the acid solution tank. The Brevik system relied upon a partial liquid-seal, to prevent escape of noxious fumes, but, in practice, the liquid seal permitted noxious fumes to escape from the treatment tank area, especially when the treatment solution has been heated to perhaps 140.degree.-180.degree. F. for milling efficiency.
The apparatus of this invention is also more adaptable to commercial production needs than the system patented by Brevik. The method and means of introducing the workpieces into the acid solution is more practicable in this invention, and could easily be automated.
This invention features a compartmentalized containment, which is flexible enough to be suited to the specialized requirements of treating or milling various materials. The compartments allow for separation of differing treatments of workpieces, and provide additionally-vented areas, relatively free of noxious fumes where personnel can inspect or handle the workpieces before, during or after treatment of the workpiece.
The term "chemical milling" as used in the specifications and claims, refers to the selective dissolution of a material by an appropriate acid solution, and encompasses such a method whether it results in etching of a material to the predetermined depth, or results in complete perforation of the material.